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Laboratory for Ocean Color Users FAQ


I am looking for all the MODIS Ocean data products. Why doesn't the GES DISC have them, and can I get them anywhere else?

The initial plans for MODIS Ocean data products were for a suite of 40 or more data products. MODIS-Terra had significant calibration problems, which affected the development of these products. A significant change in the MODIS Ocean data processing system took place in 2003, with the responsibility for producing data products from MODIS-Aqua transferring to the SeaWiFS Project, now called the Ocean Biology Processing Group (OBPG). This change resulted in a major reduction in the number of data products from MODIS, and the OBPG also undertook distribution of these data products. MODIS Ocean data products were deleted from the GES DISC archive. All of the MODIS-Aqua data products are available from the Ocean Color Web site,

http://oceancolor.gsfc.nasa.gov

MODIS-Terra provides sea surface temperature, and efforts are continuing to produce useful ocean color data products from the raw data. The GES DISC Giovanni system also provides data analysis and visualization capabilities for the MODIS-Aqua and SeaWiFS ocean color data products.


Can I see a tsunami in ocean color data from SeaWiFS or MODIS?

No. A tsunami moves too quickly to affect the biological systems in the ocean, or ocean optical properties. However, if a large tsunami affected a land area, the outflow as the tsunami receded could cause a significant suspension of coastal sediments, which might be visible in ocean color data, and this effect would last for several hours. The satellites still have to observe the correct area without clouds. The December 26, 2004 tsunami in the Indian Ocean happened to occur when the Jason-1 altimeter was observing the area, and the tsunami wave was detected as an increase in the height of the ocean surface.


Where can I find out more information about the differences between the newly-reprocessed SeaWiFS and MODIS ocean color data set, and the older version of the data set?

(Note, 03/22/2010): This FAQ entry was written while the MODIS ocean color data reprocessing was still underway in February and March 2010.  It may be modified slightly regarding MODIS data when the new data is incorporated into Giovanni.)

Many corrections were made to the SeaWiFS and MODIS data that primarily improved the chlorophyll concentration retrieval in turbid waters (which are found primarily near-shore).   SeaWiFS data was somewhat more affected by optical factors in turbid waters than MODIS data.   These corrections predominantly resulted in a reduction in the chlorophyll retrieval under such conditions, due to better discrimination between chlorophyll absorption and colored dissolved organic matter absorption (this is light absorption by those substances).

Therefore, Reprocessing 5.2 data (SeaWiFS), the previous data set, will commonly have much higher chlorophyll concentration values than R2009 data in turbid waters. These differences cannot be quantified on a pixel-by-pixel basis; however, if you utilize the "Lat-lon map of Time-averaged differences" option in our new Giovanni:

http://gdata1.sci.gsfc.nasa.gov/daac-bin/G3/gui.cgi?instance_id=ocean_month

utilizing both the R5.2 and the R2009 (SeaWiFS) data, you can illustrate the differences. I have attached a plot that I made for a meeting last month that allows you to see what this looks like.

A full summary of the reprocessing changes is found here on the Ocean Color Web, maintained by the Ocean Biology Processing Group:

http://oceancolor.gsfc.nasa.gov/REPROCESSING/R2009/
 

 


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Last updated: Nov 18, 2011 02:10 PM ET
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